Individuals with cystic fibrosis (CF) and pancreatic insufficiency (PI) are prone to fat malabsorption, putting them at risk for caloric, essential fatty acid, and choline deficiency, which, in turn, may lead to growth failure and a poorer clinical course. Many subjects with CF have essential fatty acid deficiency, characterized by decreased levels of linoleic acid and an increased triene/tetraene ratio, and an associated choline deficiency. As a key membrane phospholipid, choline is required for methyl metabolism, cholinergic neurotransmission, transmembrane signaling, lipid cholesterol transport and metabolism. Choline deficiency is associated with liver disease, apoptosis, steatosis, as well as brain and visual development abnormalities. In a previous randomized control trial, supplementation with LYM-X-SORB(TM), an organized lipid matrix containing lysophosphatidylcholine (LPC) monoglycerides, and triglycerides, has been shown to improve fatty acid status and vitamin E and retinol binding protein levels over a 12-month period and to improve both growth and pulmonary function status over 18 months in subjects with CF. We propose to conduct a randomized placebo-controlled double-blinded study to evaluate the effectiveness of the next generation LYM-X-SORB(TM) with improved palatability and mixing characteristics, on fatty acid and choline status of 78 children, ages 6.0 to 17.9 years, with CF and PI. We propose that essential fatty acid status (linoleic acid levels, triene/tetraene ratio) and choline status (phosphadytlcholine/ phosphatidytlethanolamine (PC/PE) ratio) will be normalized after 12 mos of supplementation with LYM-X-SORB(TM) in subjects receiving LYM-X-SORB(TM) (n=39) compared to those receiving placebo (n=39). We will also explore whether LYM-X-SORB(TM) supplementation will improve fat soluble vitamin status, bile composition, incidence of fatty liver, inflammatory cytokines, resting energy expenditure and respiratory quotient over 12 mos and improve pulmonary function, growth status, body composition and overall health status over 18 mos. Subjects will be recruited from five Cystic Fibrosis Centers and have four major protocol visits to CHOP (baseline, 3, 12, and 18 mos), and one visit at their home Center (6 mos). Our objective is to determine if LYM-X-SORB(TM) can be used as an acceptable, effective, supplement to correct the metabolic and physiological abnormalities associated with fat malabsorption in subjects with CF, the most commonly inherited genetic disease in Caucasians.